- Detoxification of atrazine in soils results from both chemical
hydrolysis and microbial degradation.
Infrared analysis was used
to study the hydrolysis of atrazine upon interaction with soil
and to ascertain the existence of enol, keto, and protonated-keto
forms of hydroxyatrazine.
Evolution of ¹⁴CO₂ from ¹⁴C-atrazine
and ¹⁴C-hydroxyatrazine was indicative of microbial degradation in
Objectives of this investigation were:
1) to determine the transitional forms of hydroxyatrazine in different pH environments; 2) to
establish the interactions of atrazine on
H⁺, Al³⁺, Cu²⁺- or saturated surfaces of "allophane, " montmorillonite, or "natural
montmorillonitic clay"; and 3) to ascertain the contribution of microbial degradation and chemical hydrolysis to atrazine detoxification in
three Oregon soils.
Infrared spectra provide evidence for the existence of enol,
keto, and protonated-keto forms of hydroxy-s-triazines.
The following transition is correlated with changes in pH:
1) an anionic
species at pH > 11.5, 2) an enol form between pH 11.5 and 3.3, 3) a
keto form at pH < 3.3, and 4) a protonated-keto species at pH < 0. Asymmetrical side chains (ethyl and isopropyl) of
apparently induced a doublet at 3400 and 3520 cm⁻¹ (protonated-ring
vNH), whereas the symmetrical side chains (ethyl) of
yielded a single band at 3330
cm⁻¹ in the protonated-keto forms.
Hydroxypropazine was not protonated in these experiments.
(H⁺ and Al³⁺)
on the exchange complex of montmorillonite and Coker soil clay promoted the hydrolysis of atrazine
as evidenced by a strong
hydroxyatrazine carbonyl band at 1745
in infrared spectra.
Reaction of atrazine with Ca- or Cu-montmorillonite did not produce a 1745
cm⁻¹ band, whereas
a small degree of
hydrolysis of atrazine was indicated in Cu-Coker clay by a weak
Dehydration increased the hydrolysis of atrazine as
evidenced by a more intense band at 1745 cm⁻¹ in the reaction product of Ca- or Cu-Coker soil clay plus atrazine, whereas
spectra of Ca- or Cu-montmorillonite plus atrazine were not
by dehydration. An "allophanic" colloid did not catalyze the
hydrolysis of atrazine when the exchange complex was saturated
with H⁺, Al³⁺, Ca²⁺, or Cu²⁺. "Al-allophane" was not sufficiently acidic to
protonate added hydroxyatrazine as a carbonyl band was not
in the reaction product.
Thus under acidic field conditions, one might expect the smectites to enhance the chemical hydrolysis of
atrazine while "allophanic" colloids and perhaps other amorphous
materials would be relatively inert.
Respired ¹⁴CO₂ from the ¹⁴C-ethyl
side-chain component of
atrazine represented approximately 10% of the input ¹⁴C-activity in
Parkdale-A and Woodburn soils and 4.5% in Parkdale-C and Coker
soils after 28 days of incubation.
The isopropyl side-chain and the
ring constituent of atrazine were subject to minimal attack by soil
The hydroxyatrazine ring was attacked more
readily than the atrazine ring.
Hydroxyatrazine accounted for approximately 10% of the extracted ¹⁴C-activity from ¹⁴C-atrazine-treated Parkdale-A, Parkdale-C, and Coker soils, and 40% from
Hydrolysis is considered the dominant pathway of
detoxification in the Woodburn soil, whereas detoxification of atrazine
in Parkdale-A, Parkdale-C, and Coker soils is a combination
microbial and chemical activity.